Field of the Invention
The present invention relates to a control device for an internal combustion engine for automatically stopping and restarting an operation of the engine to achieve an idling stop function, a coasting function and the like.
Description of the Related Art
Conventionally, there is known a technique for automatically stopping an operation of an internal combustion engine (i.e. a technique for automatically stopping a rotation of the engine), for example, for improving a fuel consumption and reducing an amount of an exhaust gas when a vehicle is stopped and/or is decelerated. The engine to which such a technique is applied, is referred to as the engine with an automatic stop function. In general, in order to stop the rotation of the engine by such an automatic stop function, a supply of a fuel to the engine is stopped (see a time t0 in FIG. 1). In this case, the rotation of the engine is not stopped immediately after the fuel supply is stopped and the engine continues to rotate by an inertia for a while.
As illustrated in FIG. 1, when an engine speed approaches to generally zero, a phenomenon that a direction of a rotation of the engine changes repeatedly between normal and reverse rotation directions (i.e., a back-and-forth phenomenon) after a time t1. This phenomenon occurs because a piston positioned in a certain cylinder cannot exceed a compression top dead center due to a compression reaction force in the cylinder and thus, the direction of the rotation of the engine reverses and thereafter, a piston positioned in another cylinder at a combustion stroke is subject to a compression reaction when the piston moves toward the compression top dead center. Then, at a time t2 in FIG. 1, the rotation of the engine is completely stopped. Hereinafter, a period from a time when a process for stopping the rotation of the engine starts by the automatic stop function to a time when the rotation of the engine is completely stopped (i.e., a period from the time t0 to the time t2 in FIG. 1), may be referred to as “the idle period”. Further, a period from a time which corresponds to a first reverse time (see the time t1 in FIG. 1) when the direction of the rotation of the engine first changes from a normal rotation direction to a reverse rotation direction during the idle period to a time which corresponds to a complete stop time (see a time t2 in FIG. 1) when the rotation of the engine is completely stopped after the direction of the rotation of the engine changes repeatedly between the normal and reverse rotation directions, may be referred as to “the back-and-forth period”.
On the other hand, a restart of the operation of the engine (hereinafter, this restart will be referred to as “the engine restart”) is requested, for example, when a driver depresses an accelerator pedal during the idle period. The engine restart is requested at any timing. In general, when the engine restart is requested, the operation of the engine (hereinafter, this operation will be referred to as the engine operation”) is restarted by a cranking carried out by a starter motor. In this regard, when a magnitude of the engine speed at the beginning of the cranking is excessively large, a vibration and a noise may be generated. In other words, when the engine speed at the beginning of the cranking is not within a permission range (i.e. a range between a lower limit value L which is a negative value and an upper limit value U which is a positive value) illustrated in FIG. 1, a vibration and a noise may be generated.
In particular, in general, most of the starter motors are of a type that a pinion gear provided at a tip end of a drive shaft of the starter motor is moved to mesh with a ring gear secured on a crank shaft at the beginning of the cranking. In case that such a starter motor is used, when a magnitude of the engine speed is excessively large at the beginning of the cranking, the pinion gear cannot smoothly mesh with the ring gear. As a result, a vibration and a noise are generated and there may be a problem that, for example, damage or wear of the pinion and ring gears may occur. Hereinafter, a problem such as the aforementioned vibration and wear generated due to the start of the cranking carried out by the starter motor in response to the engine restart request during the idle period may be referred to as “the problem at the beginning of the cranking”. Note that regarding a starter motor other than the starter motor of the type described above, when a magnitude of the engine speed at the beginning of the cranking is excessively large, the problem at the beginning of the cranking (in particular, the vibration and/or the noise) may occur.
In order to avoid the problem at the beginning of the cranking, the cranking carried out by the starter motor should be started when the engine speed is within the permission range.
Accordingly, a conventional device predicts the engine speed during the idle period by using a “model formula” and controls the cranking carried out by the starter motor on the basis of the result of the prediction (for example, see JP 2014-077399 A).